The present invention relates generally to the monitoring of leakage currents in an electrical power transmission system and, more particularly, to a sensor for accurately detecting and monitoring leakage current in post-type insulators.
In many countries, including the United States, wood is utilized as part of line insulation in electrical power transmission systems to improve the basic insulation level (“BIL”) of the line, as it has been recognized that the lighting performance of transmission lines can be improved by utilizing the wood support or pole. This has not been without problems as there were, and still are, many instances of fires of the wood poles and cross arms caused by low frequency leakage current and sparking on the wood from sources such as leakage current due to insulator contamination, despite mitigation measures being taken.
Insulators installed on electrical power transmission and distribution systems are exposed to contamination, for example from marine salt, road salt, and industrial pollutants. This contamination can result in flashover of the insulator, usually under light wetting conditions, e.g. condensation, when the salts and water mix to become a conductive electrolyte. Flashover is a problem in that it results in an outage which interrupts power to utility customers.
When the salts on the surfaces of an insulator become wet they form an electrolyte which is conductive. Since the one end of the insulator is energized, and the other end is grounded, leakage currents flow along the insulator surfaces. If these currents are large enough arcing will occur (called dry band arcing), this arcing will either extinguish or grow to result in a flashover. The magnitude of the leakage currents that occur under the dry band arcing conditions provide an indication of the risk of the insulator flashing over. If insulators are at risk of flashover due to contamination build-up, utilities can wash the insulators or take other measures such as redirecting power to other transmission and distribution assets.
In addition when composite (also called polymer or non-ceramic) or coated insulators are used the leakage currents and arcing on the surface can degrade the rubber material used therein.
Accordingly, there is a need for a leakage current monitoring system that continuously monitors and reports potential leakage current issues to allow an action to be taken to mitigate any potential problems that may arise from the leakage current.